RBcel1 is an endoglucanase belonging to glycoside hydrolase family 5 subfamily 5 (GH5_5) that was recently identified from a soil metagenome library from the Antarctic. Unlike its closest structural ... [more ▼]

RBcel1 is an endoglucanase belonging to glycoside hydrolase family 5 subfamily 5 (GH5_5) that was recently identified from a soil metagenome library from the Antarctic. Unlike its closest structural homologue (Cel5A from Thermoascus aurantiacus), this enzyme was reported to be able to catalyze transglycosylation reactions and has putatively been implicated in the bacterial cellulose-synthesis process. Here, the structure of RBcel1 at 1.4 A resolution, solved by molecular replacement, is reported. The structure and putative substrate-binding site are described and compared with those of other GH5_5 subfamily members. [less ▲]

The CphAII protein from the hyperthermophile Aquifex aeolicus shows the five conserved motifs of the metallo-β-lactamase (MBL) superfamily and presents 28% identity with the Aeromonas hydrophila subclass ... [more ▼]

The CphAII protein from the hyperthermophile Aquifex aeolicus shows the five conserved motifs of the metallo-β-lactamase (MBL) superfamily and presents 28% identity with the Aeromonas hydrophila subclass B2 CphA MBL. The gene encoding CphAII was amplified by PCR from the A. aeolicus genomic DNA and overexpressed in Escherichia coli using a pLex-based expression system. The recombinant CphAII protein was purified by a combination of heating (to denature E. coli proteins) and two steps of immobilized metal affinity chromatography. The purified enzyme preparation did not exhibit a β-lactamase activity but showed a metal-dependent phosphodiesterase activity versus bis-p-nitrophenyl phosphate and thymidine 5'-monophosphate p-nitrophenyl ester, with an optimum at 85°C. The circular dichroism spectrum was in agreement with the percentage of secondary structures characteristic of the MBL αββα fold. [less ▲]

The crystallographic structure of ACT-1, which is the first plasmid-mediated AmpC-type beta-lactamase to have been completely analyzed in terms of nucleotide sequence and which has a high degree of ... [more ▼]

The crystallographic structure of ACT-1, which is the first plasmid-mediated AmpC-type beta-lactamase to have been completely analyzed in terms of nucleotide sequence and which has a high degree of sequence similarity to the chromosomal AmpC enzymes of Enterobacter cloacae and the plasmid-encoded MIR-1, has been solved at 2.4 A resolution. The overall structure of ACT-1 is similar to those of other class C beta-lactamases, such as the AmpC enzymes from E. cloacae P99 and Escherichia coli. [less ▲]

The crystal structure of a cold-active aminopeptidase (ColAP) from Colwellia psychrerythraea strain 34H has been determined, extending the number of crystal structures of the M1 metallopeptidase family to ... [more ▼]

The crystal structure of a cold-active aminopeptidase (ColAP) from Colwellia psychrerythraea strain 34H has been determined, extending the number of crystal structures of the M1 metallopeptidase family to four among the 436 members currently identified. In agreement with their sequence similarity, the overall structure of ColAP displayed a high correspondence with leukotriene A4 hydrolase (LTA4H), a human bifunctional enzyme that converts leukotriene A4 (LTA4) in the potent chemoattractant leukotriene B4. Indeed, both enzymes are composed of three domains, an N-terminal saddle-like domain, a catalytic thermolysin-like domain, and a less conserved C-terminal alpha-helical flat spiral domain. Together, these domains form a deep cavity harboring the zinc binding site formed by residues included in the conserved HEXXHX(18)H motif. A detailed structural comparison of these enzymes revealed several plausible determinants of ColAP cold adaptation. The main differences involve specific amino acid substitutions, loop content and solvent exposure, complexity and distribution of ion pairs, and differential domain flexibilities. Such elements may act synergistically to allow conformational flexibility needed for an efficient catalysis in cold environments. Furthermore, the region of ColAP corresponding to the aminopeptidase active site of LTA4H is much more conserved than the suggested LTA4 substrate binding region. This observation supports the hypothesis that this region of the LTA4H active site has evolved in order to fit the lipidic substrate. [less ▲]

The heterologous production in Escherichia coli, the purification, and the kinetic characterization of four plasmid-encoded class C beta-lactamases (ACT-1, MIR-1, CMY-2, and CMY-1) were performed. Except ... [more ▼]

The heterologous production in Escherichia coli, the purification, and the kinetic characterization of four plasmid-encoded class C beta-lactamases (ACT-1, MIR-1, CMY-2, and CMY-1) were performed. Except for their instability, these enzymes are very similar to the known chromosomally encoded AmpC beta-lactamases. Their kinetic parameters did not show major differences from those obtained for the corresponding chromosomal enzymes. However, the K(m) values of CMY-2 for cefuroxime, cefotaxime, and oxacillin were significantly decreased compared to those of the chromosomal AmpC enzymes. Finally, the susceptibility patterns of different E. coli hosts producing a plasmid- or a chromosome-encoded class C enzyme toward beta-lactam antibiotics are mainly due to the overproduction of the beta-lactamase in the periplasmic space of the bacteria rather than to a specific catalytic profile of the plasmid-encoded beta-lactamases. [less ▲]

The ybxI gene of Bacillus subtilis 168 encodes a preprotein of 267 amino acid residues, including a putative signal peptide of 23 residues. The YbxI primary structure exhibits high similarity scores with two members of the superfamily of the serine penicillin-recognizing enzymes: the class D beta-lactamases and the hydrophilic carboxy-terminal domains of the BlaR and MecR penicillin receptors. To determine the function and the activity of this putative penicillin-recognizing enzyme, we have subcloned the ybxI gene in the pET-26b expression vector. Transformation of Escherichia coli BL21(DE3) by the recombinant plasmid pCIP51 resulted in the export of the mature YbxI in the periplasm as a water-soluble protein. The recombinant protein was purified to 95% homogeneity. YbxI interacts with several beta-lactam antibiotics and can hydrolyze some of them. YbxI is not inactivated by clavulanic acid. The YbxI function and its enzymatic activity in B. subtilis remain unknown. The acyl-enzyme obtained after incubation of YbxI with a fluorescent derivative of ampicillin can be detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, confirming that YbxI can be acylated by beta-lactam antibiotics. YbxI does not hydrolyze some of the standard substrates of D-alanyl-D-alanine peptidases, the targets of penicillin. YbxI belongs to the penicillin-recognizing enzyme family but has an activity intermediate between those of a penicillin-binding protein and a beta-lactamase. [less ▲]